The present invention relates to compositions useful for oxygen scavenging, particularly to substantially transparent compositions including a polyester base polymer, a blend of oxidizable polyether-based additives, and a transition metal salt as an oxidation catalyst. The polyester containers made therefrom have improved mechanical properties such as, for example, improved impact strength.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
It is well known that oxygen-sensitive food products such as tomato-based ketchups and sauces, and beverage products such as orange juice, beer, and green tea, require a packaging material that has either high oxygen barrier properties or the ability to block any oxygen ingress so as to preserve the freshness and flavor of the packaged contents. Traditionally, metal and glass packaging (e.g., cans or jars) has been used as oxygen-impervious containers.
However, in recent years, plastic containers, and more particularly injection stretch blow molded polyethylene terephthalate (PET) containers have made significant inroads into packaging, replacing the metal and glass containers for at least reasons of better economics, lighter weight, increased breakage resistance, and better consumer acceptance. Such PET containers have indeed enjoyed widespread use in packaging at least because the biaxial orientation of PET polymer chains leads to a unique combination of clarity, toughness and moderate gas barrier properties.
In barrier layers of packaging walls that are made from blends of oxygen scavenging materials with base polymer resins such as PET, a significant haze can result due to such factors as: the immiscibility of the scavenging materials with the base polymer resins, and the inability to create by mechanical blending means disperse-phase domains that are so small as not to interfere with the passage of light therethrough; and the adverse influence of the scavenging material on the crystallization behavior of PET base resin. One approach to minimizing such haze is careful selection of base resin to improve dispersibility of the scavenger material and, thus, reduce, but not substantially eliminate, haze; and to minimize the adverse crystallization effect. This approach may undesirably narrowly restrict the choice of base polymer resin. Another approach is to use compositions that serve as compatibilizers to reduce haze. These approaches add cost to the layer and the compatibilizer adds an additional material that must be evaluated for its suitability for contact with food.
Barrier materials based on polyether-polyester block copolymers have been developed that are compatible with PET and, thus, form substantially clear containers when blended with PET and blow molded into containers and which provide high oxygen scavenging capability. Such containers, however, suffer from a significant drawback in that upon impact, they become hazy. Thus, there is a need in the art for effective oxygen scavenging compositions that satisfy container clarity requirements and the impact damage-resistance requirement.